This invention relates to a fuel control system and a fuel injection timing control method for an internal combustion engine used with a vehicle such as an automobile, or in particular to a fuel control system and a fuel injection timing control method for a cylinder direct injection internal combustion engine for injecting the fuel directly into each combustion chamber.
A conventional fuel injection control system for the cylinder direct injection internal combustion engine with the fuel injected directly into the combustion chamber from a fuel injection valve (injector) has been proposed, wherein the fuel injection start timing is changed in accordance with the fuel pressure based on a map of fuel pressure versus fuel injection start timing preset in order to maintain the position unchanged at which the fuel spray injected from the injector collides with a cavity (piston depression) formed at the piston top in the combustion chamber, i.e. in order to maintain the same colliding position at a reference fuel pressure irrespective of the fuel pressure change, and wherein the injection end timing is calculated from the fuel injection start timing corrected based on the map and the fuel is injected based on these information (JP-A-2005-2896).
This fuel control system is for the cylinder direct injection internal combustion engine for combusting the compressed natural gas and can establish the stratified combustion low in robustness.
In the conventional fuel control system described above, the ignition timing remains at the basic ignition timing as long as the internal combustion engine is in steady operation, and therefore it is possible to maintain the optimum position at which the fuel spray collides with the cavity thereby to ignite the fuel spray at a predetermined position (predetermined portion).
During the idle operation or the acceleration/deceleration, however, the ignition timing is corrected with respect to the basic ignition timing and therefore an unpredicted portion of the fuel spray may be ignited for deterioration of fuel combustion.